In an exhaust gas discharged from a glass melting furnace, various components derived from a glass raw material are usually contained. For example, in a case where borosilicate glass is produced, in the exhaust gas, a boron component containing boron (B) is contained. Further, in many cases, a sulfur component containing sulfur (S) is contained. If these components are discharged to the atmosphere as they are, they are likely to present adverse influences to the environment. Therefore, various methods are being studied to remove these components from the exhaust gas.
As a method for removing a boron component and a sulfur component from an exhaust gas, Patent Document 1 discloses a method wherein a boron component and a sulfur component in an exhaust gas are removed as dissolved in water by bringing cooling water and contacting water in contact with the exhaust gas. It is so designed that a waste liquid containing the boron component and the sulfur component, formed by this method, can be reused as cooling water or contacting water after being neutralized.
In Examples in Patent Document 1, NaOH is used as a neutralizing agent, whereby no precipitate will be formed by the neutralization, and the waste liquid after the neutralization may be reused as it is, as a part of cooling water or contacting water. Further, since the boron component, etc. contained in the exhaust gas are useful as glass raw materials, it is also being studied to recover them and reuse them as glass raw materials.
Patent Document 2 discloses a method wherein as a fuel at the time of heating and melting a glass raw material, a fuel containing substantially no sulfur component is used; an exhaust gas from the glass melting furnace is contacted with water to obtain a collected liquid; the collected liquid is neutralized to obtain a neutralized collected liquid; and the neutralized collected liquid is subjected to solid-liquid separation, followed by heating and drying, to recover an arsenic component, a boron component and a chlorine component which are useful as glass raw materials.